This invention is directed to a step motor driving circuit, and in particular to a step motor driving circuit particularly suited for use in an electronic wristwatch that is capable of driving the clock hands of a wristwatch in a forward direction and in a reverse direction.
In view of the limited space provided in electronic wristwatches for the electronic movement and the battery, it is imperative that the electronic movement consume as little power as possible during operation, in order to prevent a battery from being readily dissipated over long periods of use. Accordingly, efforts are continually made to effect a further reduction in the size of the components of the electronic wristwatch and, at the same time, increase the efficiency of the components. Step motors, utilized in an electronic wristwatch for effecting an incremental driving of the gear train, in response to the electronic timekeeping signals produced by the electronic circuitry, are optimally constructed to obtain greater efficiency and reduced power consumption during operation.
Moreover, because normal timekeeping operations require that the clock hands be advanced in only a clockwise direction, in order to provide an accurate timekeeping function, the emphasis in step motor constructions has been to have same effect an incremental rotation of the clock hands in a single direction, namely, a clockwise direction. Moreover, the emphasis in improving step motors has been in reducing the current consumption of step motors capable of effecting incremental rotation of the step motor in a fixed rotational direction and not to incrementally rotating the rotor in two directions. Accordingly, miniaturized, highly efficient step motors capable of being incorporated in a miniaturized electronic wristwatch movement and further capable of imparting incremental rotary motion in two directions have heretofore not been provided.
Although concepts have been developed for effecting the rotation of a step motor in two directions, these ideas were not practical when incorporated into a miniaturized step motor of the type utilized in an electronic wristwatch. As detailed below, these constructions are often very complex, require highly toleranced components that are difficult to manufacture, and admit of increased power consumption during use. However, it has been found that the number of consumer functions, and hence the convenience and desirability of electronic wristwatches can be increased by providing miniaturized step motors in an electronic wristwatch that are capable of providing incremental rotation in two directions.